Re: [PATCH v2 03/10] pwm: imx: Rewrite imx_pwm_*_v1 code to facilitate switch to atomic pwm operation

Lukasz Majewski
2016-10-31T08:16:27Z

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Hi Sascha,

> On Thu, Oct 27, 2016 at 09:40:05AM +0200, Boris Brezillon wrote:
> > On Thu, 27 Oct 2016 08:29:39 +0200
> > Lukasz Majewski <l.majewski@majess.pl> wrote:
> >
> > > The code has been rewritten to remove "generic" calls to
> > > imx_pwm_{enable|disable|config}.
> > >
> > > Such approach would facilitate switch to atomic PWM (a.k.a
> > > ->apply()) implementation.
> > >
> > > Suggested-by: Stefan Agner <stefan@agner.ch>
> > > Suggested-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> > > Signed-off-by: Lukasz Majewski <l.majewski@majess.pl>
> > > ---
> > > Changes for v2:
> > > - Add missing clock unprepare for clk_ipg
> > > - Enable peripheral PWM clock (clk_per)
> > > ---
> > > drivers/pwm/pwm-imx.c | 50
> > > ++++++++++++++++++++++++++++++++++++++------------ 1 file
> > > changed, 38 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/drivers/pwm/pwm-imx.c b/drivers/pwm/pwm-imx.c
> > > index ea3ce79..822eb5a 100644
> > > --- a/drivers/pwm/pwm-imx.c
> > > +++ b/drivers/pwm/pwm-imx.c
> > > @@ -65,8 +65,6 @@ struct imx_chip {
> > > static int imx_pwm_config_v1(struct pwm_chip *chip,
> > > struct pwm_device *pwm, int duty_ns, int
> > > period_ns) {
> > > - struct imx_chip *imx = to_imx_chip(chip);
> > > -
> > > /*
> > > * The PWM subsystem allows for exact frequencies.
> > > However,
> > > * I cannot connect a scope on my device to the PWM line
> > > and @@ -84,26 +82,56 @@ static int imx_pwm_config_v1(struct
> > > pwm_chip *chip,
> > > * both the prescaler (/1 .. /128) and then by CLKSEL
> > > * (/2 .. /16).
> > > */
> > > + struct imx_chip *imx = to_imx_chip(chip);
> > > u32 max = readl(imx->mmio_base + MX1_PWMP);
> > > u32 p = max * duty_ns / period_ns;
> > > + int ret;
> > > +
> > > + ret = clk_prepare_enable(imx->clk_ipg);
> > > + if (ret)
> > > + return ret;
> > > +
> > > writel(max - p, imx->mmio_base + MX1_PWMS);
> > >
> > > + clk_disable_unprepare(imx->clk_ipg);
> > > +
> > > return 0;
> > > }
> > >
> > > -static void imx_pwm_set_enable_v1(struct pwm_chip *chip, bool
> > > enable) +static int imx_pwm_enable_v1(struct pwm_chip *chip,
> > > struct pwm_device *pwm) {
> > > struct imx_chip *imx = to_imx_chip(chip);
> > > + int ret;
> > > u32 val;
> > >
> > > + ret = clk_prepare_enable(imx->clk_ipg);
> > > + if (ret)
> > > + return ret;
> > > +
> > > + ret = clk_prepare_enable(imx->clk_per);
> > > + if (ret)
> > > + return ret;
> > > +
> > > val = readl(imx->mmio_base + MX1_PWMC);
> > > + val |= MX1_PWMC_EN;
> > > + writel(val, imx->mmio_base + MX1_PWMC);
> > >
> > > - if (enable)
> > > - val |= MX1_PWMC_EN;
> > > - else
> > > - val &= ~MX1_PWMC_EN;
> > > + clk_disable_unprepare(imx->clk_ipg);
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +static void imx_pwm_disable_v1(struct pwm_chip *chip, struct
> > > pwm_device *pwm) +{
> > > + struct imx_chip *imx = to_imx_chip(chip);
> > > + u32 val;
> > > +
> > > + val = readl(imx->mmio_base + MX1_PWMC);
> > > + val &= ~MX1_PWMC_EN;
> > >
> > > writel(val, imx->mmio_base + MX1_PWMC);
> >
> > Are you sure you don't need to enable the ipg clk when manipulating
> > the PWMC register?
> > If it's not needed here, then it's probably not needed in
> > imx_pwm_enable_v1() either.
>
> As said, even the commit 7b27c160c68 introducing the register clk did
> not enable the clock consistently for all register accesses.

If I might ask - do you have i.MX hardware with PWMv1? If yes, I would
be grateful for testing (and provide proper patch), since I don't posses
one.

> Maybe
> it's best to include the following patch so that we can find a clear
> culprit

If we don't have HW to test the solution - why should we apply this
patch and introduce regression?

If you can provide (and test) fix for v1 - please prepare patch, so it
could be added on top of this patch series (as done with pwm polarity
inversion in this patch series).

> and do not bury the ipg clock changes in larger patches.
>
> Sascha
>
> -----------------------------8<-----------------------------------
>
> From 30b77e83269a58c2cb5ce6de8be647e027030d34 Mon Sep 17 00:00:00 2001
> From: Sascha Hauer <s.hauer@pengutronix.de>
> Date: Mon, 31 Oct 2016 06:45:33 +0100
> Subject: [PATCH] pwm: imx: remove ipg clock
>
> The use of the ipg clock was introduced with commit 7b27c160c6. In the
> commit message it was claimed that the ipg clock is enabled for
> register accesses. This is true for the ->config() callback, but not
> for the ->set_enable() callback. Given that the ipg clock is not
> consistently enabled for all register accesses we can assume that
> either it is not required at all or that the current code does not
> work. Remove the ipg clock code for now so that it's no longer in the
> way of refactoring the driver.
>
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> Cc: Philipp Zabel <p.zabel@pengutronix.de>
> ---
> drivers/pwm/pwm-imx.c | 19 +------------------
> 1 file changed, 1 insertion(+), 18 deletions(-)
>
> diff --git a/drivers/pwm/pwm-imx.c b/drivers/pwm/pwm-imx.c
> index d600fd5..70609ef2 100644
> --- a/drivers/pwm/pwm-imx.c
> +++ b/drivers/pwm/pwm-imx.c
> @@ -49,7 +49,6 @@
>
> struct imx_chip {
> struct clk *clk_per;
> - struct clk *clk_ipg;
>
> void __iomem *mmio_base;
>
> @@ -204,17 +203,8 @@ static int imx_pwm_config(struct pwm_chip *chip,
> struct pwm_device *pwm, int duty_ns, int period_ns)
> {
> struct imx_chip *imx = to_imx_chip(chip);
> - int ret;
> -
> - ret = clk_prepare_enable(imx->clk_ipg);
> - if (ret)
> - return ret;
>
> - ret = imx->config(chip, pwm, duty_ns, period_ns);
> -
> - clk_disable_unprepare(imx->clk_ipg);
> -
> - return ret;
> + return imx->config(chip, pwm, duty_ns, period_ns);
> }
>
> static int imx_pwm_enable(struct pwm_chip *chip, struct pwm_device
> *pwm) @@ -293,13 +283,6 @@ static int imx_pwm_probe(struct
> platform_device *pdev) return PTR_ERR(imx->clk_per);
> }
>
> - imx->clk_ipg = devm_clk_get(&pdev->dev, "ipg");
> - if (IS_ERR(imx->clk_ipg)) {
> - dev_err(&pdev->dev, "getting ipg clock failed with
> %ld\n",
> - PTR_ERR(imx->clk_ipg));
> - return PTR_ERR(imx->clk_ipg);
> - }

And in that way also v2 would be affected.

My gut feeling now is that the "community" wants to solve too many
issues with PWM atomic support rework.

Why cannot we add patches on top of already done work, but require
large patch series to be rewritten and resend ?

> -
> imx->chip.ops = &imx_pwm_ops;
> imx->chip.dev = &pdev->dev;
> imx->chip.base = -1;

Best regards,

Łukasz Majewski

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